/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Map;
import java.util.Set;
import javax.annotation.Nullable;

/**
 * A bimap (or "bidirectional map") is a map that preserves the uniqueness of its values as well as
 * that of its keys. This constraint enables bimaps to support an "inverse view", which is another
 * bimap containing the same entries as this bimap but with reversed keys and values.
 *
 * <p>
 * See the Guava User Guide article on
 * <a href= "https://github.com/google/guava/wiki/NewCollectionTypesExplained#bimap">
 * {@code BiMap}</a>.
 *
 * @author Kevin Bourrillion
 * @since 2.0
 */
@GwtCompatible
public interface BiMap<K, V> extends Map<K, V> {
    // Modification Operations

    /**
     * {@inheritDoc}
     *
     * @throws IllegalArgumentException if the given value is already bound to a different key in
     *         this bimap. The bimap will remain unmodified in this event. To avoid this exception,
     *         call {@link #forcePut} instead.
     */
    @CanIgnoreReturnValue
    @Override
    @Nullable
    V put(@Nullable K key, @Nullable V value);

    /**
     * An alternate form of {@code put} that silently removes any existing entry with the value
     * {@code value} before proceeding with the {@link #put} operation. If the bimap previously
     * contained the provided key-value mapping, this method has no effect.
     *
     * <p>
     * Note that a successful call to this method could cause the size of the bimap to increase by
     * one, stay the same, or even decrease by one.
     *
     * <p>
     * <b>Warning:</b> If an existing entry with this value is removed, the key for that entry is
     * discarded and not returned.
     *
     * @param key the key with which the specified value is to be associated
     * @param value the value to be associated with the specified key
     * @return the value which was previously associated with the key, which may be {@code null}, or
     *         {@code null} if there was no previous entry
     */
    @CanIgnoreReturnValue
    @Nullable
    V forcePut(@Nullable K key, @Nullable V value);

    // Bulk Operations

    /**
     * {@inheritDoc}
     *
     * <p>
     * <b>Warning:</b> the results of calling this method may vary depending on the iteration order
     * of {@code map}.
     *
     * @throws IllegalArgumentException if an attempt to {@code put} any entry fails. Note that some
     *         map entries may have been added to the bimap before the exception was thrown.
     */
    @Override
    void putAll(Map<? extends K, ? extends V> map);

    // Views

    /**
     * {@inheritDoc}
     *
     * <p>
     * Because a bimap has unique values, this method returns a {@link Set}, instead of the
     * {@link java.util.Collection} specified in the {@link Map} interface.
     */
    @Override
    Set<V> values();

    /**
     * Returns the inverse view of this bimap, which maps each of this bimap's values to its
     * associated key. The two bimaps are backed by the same data; any changes to one will appear in
     * the other.
     *
     * <p>
     * <b>Note:</b>There is no guaranteed correspondence between the iteration order of a bimap and
     * that of its inverse.
     *
     * @return the inverse view of this bimap
     */
    BiMap<V, K> inverse();
}
